Electrical measuring instrument.



W. J. LLOYD & L. WILSON. ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED MAY 21, 1907.

Patented June 15, 1909.

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W. J. LLOYD & L. WILSON.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED MAY 21, 1907.

925 ,1 1 3 Patented June 15, 1909.

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W. J. LLOYD & L. WILSON.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED MAY 21 107 Patented June 15, 1909.

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WILLIAM J (LLOYD, OF RUGBY, ENGLAND, AND LEONARD WILSON, OF DENVER,COLORADO,

ASSIGNORS, BY MESNE ASSIGNMENTS,'TO GENERAL ELECTRIC COMPANY, A CORPORA-TION OF NEW YORK.

ELECTRICAL IKEASI'J'IIRJITC-I- INSTRUIEN'I.

Patented June 15, 1909.

Application filed Kay 21, 1907. Serial No. 874,909. I

To all whom it may concern:

Be it known that we, WILLIAM J. LLOYD, a citizen of the United States,residing at Rugby, England, and LEONARD WILSON, a sub'ect of the King ofGreat Britain, residing at enver, county of Denver, State of 0010- rado,have invented certain new and useful Improvements in ElectricalMeasuring Instruments, of which the following is a specification.

Our invention relates to electrical measuring instruments andparticularly to instruments intended for indicating or for recording thevalues of current or electromotive force in direct current circuits. 7

In electrical instruments of a certain type, the-current to be measured,or a current proportional to the current or to the electromotive forceto be measured, passes through a conductor arranged for movement in amagnetic field. This results in a tendency to movement of the conductorand, if this movement is (apposed by a suitable countertorque, the deection from zero osition may serve to indicate the value of t e currentor electromotive force to be measured, the instrument, of course, beingproperly calibrated for this purpose.

The torque exerted by the current carrying conductor is ro ortional tothe strength of the magnetic el and the current passing in theconductor, and the strength of the field being generally constant, thetorque is directly proportional to the current passing in the conductor.In instruments of this type it is often desirable to have a strongtorque exerted by the moving element. For

this purpose instead of a permanent field.

magnet an electromagnet may be used, the current therefor being takenfrom any suitable source. It is at once evident that unless thepotential a plied to the windings of the electromagnet e constant, thestrength of the field produced by it will vary, thereby interfering withthe accuracy of the readings on the instrument.

One of the objects of our invention is to provide an instrument having ahigh torque produced bya strong field which, although it may vary instren th, will have noeffect on the accuracy of t e readings. That is,to

provide means for compensating for any variations in the excitingvoltage applied to the field coils where an electromagnet is used, ormeans for compensating for deterioration of a permanent field magnetwhen such a magnet is used.

Another object of our invention is the roduction of an instrument havinga uni orm scale and practically no error due to hysteresis and one whichis not affected by magnetic fields in its vicinity.

Other objects of our invention will be brought out in the followingdescription.

In order that our invention may be fully understood, we have shown anddescribed one form of instrument in which it may be embodied. The typeof instrument which We have chosen for this purpose is What is known asa curve drawing instrument, and it is for instruments of this kind, .inwhich a strong torque is desired in order that the friction of the .penma be negligible, that our invention is articu arly usefu We wish itistinctly understood, however, that We realize that our invention isequally applicable to indicating instruments in which a pointer attachedto the moving element moves over a scale on which the values of currentor electromotive force corresponding to different deflections of theneedle are indicated.

It is our intention to include all such applibeing removed; Fig. 2 is aplan view in crosssection on line 2-2 of Fig. 1; Fig. 3 is an ele--vation partly in section of the moving elethe instrument and thesupporting ment 0 bearings therefor; Fig. 4 is a plan view of the movingelement shown in Flg. 3 taken just below the top bearing, certain of theparts .being broken away; Fig. 5 is a view in erspective of one of theelectromagnets an its supportin frame; and Fig. 6 is a view inperspective s owing the side plates which su port the electroma nets andone ofthe she which form paths or the flux from one magnet to the other.

The working parts of the instrument illustrated are mounted on asuitable base 1 and inclosed by a casing preferably having glass sidesshown in cross-section at 2. This curve drawing instrument consists oftwo separate and distinct elements. One of these, the time recordingelement which is sup orted on the frame A, serves to move a recor sheetat a definite uniform rate of speed so that the movement of the pen,response to the energy variations to be recorded, will trace a curvefrom which the value of the current or electromotive force at any hourof the day may be determined. This time recording element may be of anyap roved construction. The other element 0 this curve drawmg instrumentis shown at the left side of the casing in Fig. 1 and serves to move theen in response to the variations in energy to e recorded. It is to thiselement that our invention particularly relates.

Referring to Figs. 1, 2, 5 and 6, the side plates 3 and 4 are connectedin any suitable way as by screws 5 to a curved shell 6 attached to thebase-board 1 in any suitable manner. The side plates 3 and 4 are bridgedat the top and bottom by the yokes 7 and 8 which support the upper andlower bearings for the moving element, said yokes being attached to theside plates by the screws 9 or otherwise. Adapted to slide in the curvedrecesses 11 of the side plates 3 and 4 is aT- shaped frame consisting ofthe curved ends 12 connected by the web 13. The parts 12 slide into andare secured in the recesses 11 and the web 13 supports the core of amagnet which forms part of the magnetic system. These field magnets, ofwhich there are two and which are similarly supported by T- shapedframes adapted to s1de in the recesses 11, each consist of a core 15which carries exciting coils 16 and at each end the curved pole pieces17, the outer curved surfaces of which are concentric with the innercurved surfaces of the shell 6 and the shell 18. The pole pieces 17carry supplementary pole pieces 19 of the form shown in Figs. 2 and 5,the purpose of which will be more fully hereinafter described. The upperand lower magnets are so wound that their adjacent pole pieces are ofopposite polarity; that is, at the back of the instrument upper poleiece 17 may have a north polarity while the ower pole piece 17 on thatside will have a south polarity and the polarity of the pole pieces onthe front side will be south at the top and north at the bottom. It isobvious that this arrangement will result in produc in a magneticcircuit through the cores and po e pieces of the magnets and the softsteel shells 6 and 18. There will thus be produced at four points,between the pole pieces 17 and the shells 6 and 18 strong annular fieldsof uniform density. The current carrying conductor is mounted formovement in these fields which by their arrangement make the instrumentastatic.

The moving element of our device is most clearly shown in Figs. 1, 3 and4. It consists primarily of two coils 20 and 21 which are mounted formovement in the annular fields heretofore described. In the instrumentshown, which is intended to be used as an ammeter, these coils eachconsist of a number of turns of large insulated condv" suitably boundtogether by the clamps 22 and 23. These coils may be supported in ansuitable manner.

11 the particular construction illustrated, the coils are connectedtogether by a small hollow shaft 24 and have attached to the top of thecoil 20 a small hollow shaft 25 and at the bottom of the coil 21 ahollow shaft 26. A bar 27 may connect the clamps 23 at the bottom of thecoil 21 and have at its center a hole through which the shaft 26 maypass. The moving element is suspended from the yoke 7 by a fine wire 30which is connected to an adjustable button 31 suitably supported in acavity at the to of the yoke 7. This wire 30 extends throug the hollowshaft 25, the shaft 24, and is secured within the hollow shaft 26 in anysuitable manner. A fine steel pin 32 projecting from the bottom of theshaft 26 into a ring stone jewel bearing 33 serves to keep the coils inproper alinement. Supported by the shaft 25 and the clamp 23 at the topof the coil 20, is a light frame composed preferably of two aluminumtubes 35 and 36 connected at their outer ends by the yoke 37 whichcarries, ivoted as shown in Fig. 3, an arm 38 at t e end of which is thepen which moves over the record sheet and traces the curve whichindicates the variations in the energy to be measured. This arm 38 iscaused to bear against the record sheet by the pull exerted by thebellcrank lever 39 carrying the adjustable weight 40 and connected tothe arm 38 by a thread 41. The arms 35 and 36 and the parts carriedthereby are counter-weighted y the weight 42 threaded on a rod 43carried by a thin U-shaped member 44 attached to the enlarged ends ofthe tubular shafts 35 The inner adjustably held thereon by screws 55.The

form.

. brought up alongside the shaft 25 as shown- It is obvious that thecontrol pieces 60.

tend to locate themselves at the point in the field between the polepieces 19 where the width of these pole pieces and therefore the numberof lines of force is the greatest. This corresponds to the zero positionof the instrument indicated by the-line 0-0 in Fi 2. Upon the shape andosition of the pole pieces 19 and the contro pieces depends theuniformity of the scale of the instrument and it has been found thatwhen these parts are roportio-ned as shown, a, scale is produced whichis practically uni The coils 20 and 21 are so wound that they may beconnected together, as shown at 64 and 65 in'Figs. 2 and 3, thus formingwhat is in eflect a single conductor. The ends are in Figs 2 and 3 andindicated at 66-and 67.

To these ends 66 and 67 are connected fiat' flexible conductors 68 and69 which are fas tened to flat plates 70 and 71 attached to butinsulated from the yoke 7 as shown in Fig. 1. The plates 70 and 71 areconnected respectively to conductors 72'and 73 which lead to theterminals 75 and 74. It is to these terminals that the current to bemeasured, or a current proportional to the current or to theelectromotive force to be measured, is applied. v

In the instrument illustrated, which is an arnmeter, the necessarydamping is obtained from the current carrying coils themselves which,being connected across a low resistance shunt 1n the usual manner, act.as a short-clrculted turn of low resistance. In a voltmeter constructedaccording to our inductors 76 and 77 are connected across the terminals78 and 79. These terminals are attached to the source of current usedfor the excitation of the fields. The coils 16 on the cores 15 are ofsuch a number of turns that at a certain normal exciting voltage thesaturation of the magnetic circuit is carried up so far that a variationin voltage, even as great as 25% above or below normal, produces achange in field strength of not more than 6%. The pole pieces 19 and thecontrol pieces 60 are so proportioned and arranged that the fieldexisting at that point is weak torque.

and the control )ieces are unsaturated. The purpose of this constructionwill be hereinafter explained. v I

The mode and theory of operation of the instrument, which we havedescribed and in which is embodied our invention, are as follows: Undernormal conditions assuming that the voltage ap lied to the fieldwindings is maintained at w at has been taken as the normal value, andthe coils 20 and 21 correctly wound according to principles which arewell understood by those skil ed in the electrical art, these 'coilswill move from their zero position .against the countertorque exertedupon them and will take up a position in the annular fields dependingupon the amount of current which is passing through them. The springs 50and 51 are so designed that they will exert a countertorque equalapproximately to one-half of the counter-torque necessary at normalexcitation voltage. designed that it exerts at normal excitation voltagea counter-torque equal to that exerted by the s rings, thus supplyingthe other .half of t e total counter-torque required when the fieldstrength is normal.

In order that the readings on the instrument shall be unaffected bychanges in exciting voltage, the total counter-torque exerted on themoving element must vary in the same pro ortion as the. armature torque.In other wor 's, assuming that a certain our- The magnetic control is sorent is flowing in the moving coils, in order 7 that the coils maystandstill while the exciting voltage, and therefore the field strengthand the armature torque varies, the total counter-torque exerted on themoving coils must vary at the same rate as does the armature tor ue.This result is attained by the use of t e combined spring and magneticcontrol heretofore described.

As has been stated, the control pieces 60 move in a weak field and areunsaturated. The torque exerted by them therefore varies approximatelyas the square of the field strength. Thus while the armature tor uevaries directly as the strength of the fie d, part of the counter-torquevaries as the square of the strength of the field.

Since the percentage variation in field strength is small the square ofsuch percentage variation is practically equal to twice such percentagevariation. It is obvious therefore that any percentage change ofarmature torque, due to change in field strength, is opposed by a changeof twice the percentage in half the total counter-torque,

or the same percentage in the whole counter- TlllS may be understoodfrom the following exam le: Suppose the current in the moving cois'to-be fixed, and suppose that at normal exciting voltage the armaturetorque is 800 gm. mm. This armaturetorque is opposed by a counter-torqueof. 400

gm. mm. due to the springs 50 and 51 lus a counter-torque of 400 gm. mm.exerte by the magnetic control.

As has been before stated, the magnetic system is so designed thatvariations in exciting voltage of 25% above or below normal produceonly-6% variation in field strength.

-Assurning now that the exciting current rises to 25% above normal,thereby roducing a 6% increase infield strength. T e armature torquewill increase in the same proportion as the field strength. or to 1.06 X800 848 gm. mm. This armature torque will now beo posed by the constantcounter-torque of t e springs,namely,400 gm. mm. plus the countertorqueexerted by the magnetic control which has increased in proportion to thesquare of the field strength and is now (1.06) X400 448 gm. mm.(approximately), making the total counter-torque 400 X 448 848 gm. mm.It is thus evident that the counter-torque has increased at the samerate as the armature torque and the coils remain inthe same osition, aswith normal exciting voltage. his same result holds true for a drop inexciting voltage up to 25% and our instrument therefore gives accuratereadings even when the fields are excited from a circuit on which thepotential varies considerably.

What we claim as new and desire to secure by Letters Patent of theUnited States, is,

1. In an electrical measuring instrument,

. means for producing a magnetic field of variable strength, a currentcarr ing conductor mounted to move in said fie d, a spring forfurnishing counter-torque to the moving conductor, and a magneticcontrol res onsive to variations in the strength of sai field for addingto the countertorque of the spring a countertorque which keeps aconstant relation between the total countertorque and the fieldstrength.

2. In an electrical measuring instrument, means for producing twomagnetic fields, a conductor arranged for movementin one of said.fields, and means forfurnishing a counter-torque to said movingconductor comprising a spring and an unsaturated magnetic control piecemoving with the conductor in the other magnetic field.

3. In an electrical measuring instrument, common means for producing twomagnetic fields of differentstrength, a current-carrying conductor arraned for movement in the stronger of said elds, a spring for exerting partof the necessary counter-torque on the moving conductor, and anunsaturated magnetic control piece responsive to the weaker.

of said fields to furnish a counter-torque which varies with thestrength of the field at such a rate that the relation of the totalcounter-torque to the strength of the stronger field is always the same.

4. In an electrical measuring instrument, means for producing a magneticfield, acurrent carrying conductor arranged for movement in said field,a spring which exerts approximately one-half ofthe necessarycounter-torque when the field strength is normal, and a magnetic controlwhich at normal field strength furnishes counter-torque equal to thatexerted by the spring but which as the I field strength varies exerts acounter-torque which keeps the relation of the total countertorque tothe main field strength always the same. 1

5. In an electrical measuring instrument, an electromagnet for producinga magnetic field, a current carrying conductor arranged for movement insaid field, a s ring which furnishes approximately ODE-llfil? of thenecessary counter-torque to the moving conductor at normal excitationvoltage, and a magnetic control responsive to variations'in excitationvoltage which at the normal excitation voltage furnishes approximatelyonehalf the counter-torque but which at voltages other than the normalvoltage exerts a counter-torque which keeps the relation of the totalcounter-torque to the field strength always the same.

6. In an electrical measuring instrument, means for producing a magneticfield of high magnetic ensity and a second field of low magneticdensity, a current carrying conductor arran ed for movement in saidfirst mentioned fie d, a spring for exerting on the movconductor part ofthe necessary counter torque, and a magnetic control piece movable withthe conductor in the second mentioned field and serving to furnish theremainder of the necessary counter-torque.

7. In'an electrical measuring instrument, means for roducing a magneticfield of high magnetic ensity and a second field of low magneticdensity, a current carryin conductor arranged for movement in said rstmentioned field, a spring for exerting approximately onezhalf of thenecessary counter.- torque when the field strength is normal, and amagnetic control which at normal field strength furnishes counter-torqueequal to that exerted by the spring but as the field strength variesexerts a counter-torque which kee s the relation of the totalcounter-torque to tlie main field strength always the same.

8. In an electrical measuring instrument, an electromagnet for producinga' magnetic field of high magnetic density and a second field of lowmagnetic density, a current carrying conductor arranged for movement in.said first mentioned field, a s rin which furnishes approximately one-haf o? the necessary counter-torque. to the moving conductor at normalexcitation voltage, and a magnetic control which at the normalexcitation voltage furnishes approximately one-half the counter-torquebut which at voltages other than the normal voltage exerts acountertorque varying with the voltage to keep the variations in thestrength 0 the first field.

i relation of the total counter-torque to the field strength always thesame. I

9. In an electrical measuring instrument, a magnetic system having acurved field of force,-a current carrying conductor arranged formovement in said curved field, and means for exerting a counter-torqueon said moving conductor which will vary in proportion to variations inthe strength of the curved field.

10. In an electrical measuring instrument, means for producing twocurved magnetic fields having a common axis, a current carryingconductor arrangedfor movement in oneof said fields, and a combinedspring and magnetic control for the-moving conductor comprising amagnetic member mounted on said conductor to move in the other of saidfields.

11. In an electrical measuring instrument, a magnetic system having twocurved fields of force with a common axis, a current-carrying conductorpivoted at said axis to move in one of said fields, a spring forexerting a counter-torque on said conductor, and amagnetic control iecepivoted to move in the other of said elds to furnish acountertorquewhich will vary'in roportion to the 12. In an electricalmeasuring instrument, a magnetic system having two adjacent fields offorce, one of said fields'being curved, a current carrying conductorarranged for movement in said curved field, a spring for exerting acounter-torque on said moving conductor, and a magnetic control iecearranged to respond to variations in t e other of said fields to exertan additional countertorque on said moving conductor.

13. In an electrical measuring instrument, a magnetic system having acurved field of force, a current carrying conductor arran ed formovement in said curved field, a sprmg for exerting on the movingconductor part of the necessary counter-torque, and a magnetic controlwhich furnishes counter-torque which varies with the strength of thecurved field at such a rate that the relation of the totalcounter-torque to the main field strength is always the same. a i

14. In an electrical measuring instrument, a magnetic system having anannular field of force of high magnetic density and a second field oflow magnetic density, a current carrying conductor arranged for movementin said annular field, a spring for exerting on the moving conductorpart of the necessary counter-torque, and a magnetic control piecemovable with the conductor in the second mentioned field and serving tofurnish the remainder of the necessary counter-torque.

15. In an electrical measurin instrument, means for producing an annu armagnetic field of force comprismg two ma nets having curved ole facesconcentric to t e same axis and a s fiell arranged adjacent each pairvof curved pole faces and concentric therewith, a current carryingconductor arranged for movement in said annular field, a spring forexerting part of the necessary counter-torque on the movmg conductor,and a magnetic control piece moving with said conductor in a magneticfield between the two magnets for furnishing the rest of the necessarycountertorque.

16. In an means for producing an annular magnetic field of force of highmagnetic density and a second field of low magnetic density com rismgtwo-magnets having curved ole aces concentric to the same axis, a sheladjacent each pair of curved pole faces'and concentric therewith, poleieces attached to the adjacent sides of eacli pair of pole faces, acurrent carrying conductor arranged for movement 1n said annular field,a spring for exerting part of the necessary counter-torque on the movingconductor, and a magnetic control piece movin with said conductor inthesec- 0nd field of orce between the pole pieces.

17. In an electrical measuring instrument, a magnetic system comprisingtwo cores having curved gole faces and arranged with their axis paralland with their curved pole faces in the same plane, a shell arran edadjacent and parallel to each 1pair of pole faces, a magnetizing coil oneac core so arranged as to magnetize the adjacent pole faces of thecores oppositely, a current carrying conductor arranged with two aproximately rectangular coils connected toget er one coil surroundingeach core, a spring for, furnishing part of the necessary counter-torue, and a magnetic control piece arranged etween the rectangular coilsand moving in the magnetic field between the cores.

18. In an electrical measuring instrument, a magnetic system comprisingtwo cores having curved pole faces and arranged with their axes paralleland with their curved pole faces in the same plane, a shell arran edadjacent and parallel to each air of pole aces, a magnetizing coil oneac core so arranged as to magnetize the adjacent pole faces ofthe coresoppositely, ole pieces attached to the adj acent sides 0' each pair ofpole faces, a current carr 'n conductor arranged for movement in t eelds between the shell and the pole faces, and a magnetic control iecemovable with said conductor in a fiel pole pieces.

19. In an electrical measuring instrument, a magnetic system comprisingtwo electromagnets arranged with their axes parallel and having curvedpole faces arranged in the same plane, the adjacent pole faces beingmagnetized oppositely, a shell arranged adjacent each pair of polefaces, horn-shaped pole pieces attached to the adjacent sides'of eachpair of pole faces, a current carrying conductor arranged for movementin the electrical measuring instrument,

between the fields between said pole faces and said shells, andwedge-shaped control pieces movable with said coil in the fields betweensaid hornshaped pole pieces.

20. In an electrical measuring instrument, a magnetic system comprisingtwo magnets having curved .pole faces concentric to the same axis, and ashell arranged adjacent each pair of curved pole faces and concentrictherewith.

21. In an electrical measuring instrument, a magnetic system comprisingtwo cores having curved pole faces and arranged with their axes paralleland with their curved pole faces in the same plane, and a shell arrangedadj acent and parallel to each pair of pole faces.

22. In an electrical measuring instrument, a magnetic system comprisingtwo cores having curved pole faces and arranged with their axes paralleland with their curved pole faces in the same plane, a shell arrangedadjacent and parallel to each pair of pole faces, a magnetizing coil oneach core so arranged as to magnetize the adjacent pole faces of thecores oppositely, and a current carrying conductor arranged for movementin the fields between the pole faces and shells.

23. In an electrical measuring instrument, a magnetic system comprisingtwo magnets having curved pole faces concentric to the same axis, ashell arranged adjacent each pair of curved pole faces and concentrictherewith, and pole pieces attached to the adjacent sides of each pairof curved pole faces.

24. In an electrical measuring instrument, a magnetic system comprisingtwo magnets having curved pole faces concentric to the sam'e axis, \ashell arranged adjacent each pair of pole faces and concentrictherewith, and horn-shaped pole pieces attached to the pdjacent sides ofeach pair of curved pole aces.

25. In an electrical measuring instrument,

a magnetic system comprising two cores hav ing curved pole faces andarranged with their axes parallel and with their curved pole faces inthe same plane, a shell arranged adjacent and parallel to each pair ofpole faces, a magnetizing coil on each core so arranged as to magnetizethe adjacent pole faces of the cores oppositely, and pole piecesattached to the ad acent sides of each pair of pole pieces.

26. In an electrical measuring instrument, a movable element comprisingtwo coils connected in series and arranged in the same plane, andmagnetic control pieces supported between said coils.

27. In an electrical measuring instrument, a movable system comprisingtwo coils connected in series and arranged in the same plane, andwedge-shaped magnetic control pieces supported between said coils.

In witness whereof, LLOYD has hereunto set his hand this 24th day ofApril, 1907 and WILSON has hereunto set his hand this 14th day of May,1907.

